TRIS(2-ETHYLHEXYL) PHOSPHATE AND TRICRESYL PHOSPHATE AS NEW NEUTRAL CARRIERS FOR ORGANIC AMMONIUM ION-SELECTIVE MEMBRANE ELECTRODES

Phosphate esters, such as tris(2-ethylhexyl) phosphate (TEHP) and tric resyl phosphate, can be used as neutral carriers to make organic ammon ium ion-selective membrane electrodes. For example, a hexylammonium io n-selective electrode was constructed using TEHP as the carrier and di octyl phthalate as a membrane solvent in a poly(vinyl chloride) membra ne matrix. The electrode exhibited a near-Nernstian response to hexyla mmonium in the concentration range from 2x10(-4) to 0.1 M with a slope of 57 mV per concentration decade. The lower limit of detection was 2 x10(-5) M, was comparable to that of the electrode made from one of th e amine ionophores, a calix[6]arene analog, reported previously. The i nteraction between the phosphate ester and hexylammonium was confirmed by H-1-NMR spectroscopy. (C) 1997 Elsevier Science B.V.